The general objective of our research is to study the biological language. We investigate language and its formal architecture, its acquisition, and its representation in the brain, by studying languages which have arisen outside of the mainstream of human spoken languages; the visuospatial gestural systems of deaf people. We contrast children with different early language and sensory experiences: deaf children of deaf parents (DD) who learned sign as a native language; hearing children of deaf parents (HD), and deaf children of hearing parents (DH) who are profoundly deaf and had no signing experience for the first few years of life, but are now exposed to a rich signing ASL environment. I. The Acquisition of Spatial Language. The study of the acquisition of American Sign Language (ASL) in young children brings into focus some fundamental questions about the representation of language and the representation of space. We investigate the development of spatial language, including the onset of signing, and the acquisition of the spatial organization underlying syntax and discourse. We investigate the development of the use of space to represent syntactic relations as opposed to the use of space to represent real world spatial relations. These studies will incidentally provide an important instrument for reliably measuring the onset of signing across different populations. II. The Interplay between Spatial Language and Spatial Cognition. The young deaf child is faced with the dual task in sign language of spatial perception, memory and spatial transformations, on the one hand, and processing grammatical structure on the other, all in one and the same visual event. Children with different auditory and language experience who learn sign as a first language provide a privileged testing ground for investigating the interplay between development of a spatial language and its spatial cognitive underpinnings. We investigate whether the complex requirements for spatial processing affect the development of particular spatial cognitive capacities, and parse out the effects of different sensory and language experiences. III. The Development of Neural Systems Underlying Spatial Language and Cognition. Language and spatial representation are attributes for which the two hemispheres in deaf people show different specializations, as our research has shown. In a series of studies we directly examine the development of brain organization for language and space. Experimental studies address the link between early hand dominance for sign and brain organization, experimental probes of spatial language and spatial cognition, and event related potential studies of the neural systems underlying the onset of signing in deaf infants. These studies will allow an understanding of the determinants of brain organization for higher cognitive functions.